Lead-chelating hole-transport layers for efficient and stable perovskite minimodules

Spiro-Linked Planar Core Small Molecule Hole Transport Materials Enabling High-Performance Inverted Perovskite Solar Cells

Small-molecule organic semiconductors have demonstrated significant potential for application in hole-transporting materials (HTMs) for perovskite solar cells (PSCs), thanks to their high reproducibility and convenient synthesis routes. Finely designed planar π-π stacking structures have emerged as one of the primary strategies for achieving high-performance small-molecule HTMs. In particular, the incorporation of a helical structure into HTM designs through a linearization approach has proven effective, leading to the development of novel materials with superior properties. In this study, the structure-property relationship of these small molecules has been systematically explored. The newly developed HTM, SPCF-MeTPA, based on a spiro[cyclopentane-1,9'-fluorene] core, features a rigid conjugated system with spiro-linked core. This design provides improved intermolecular charge extraction and transport, optimized energy levels, and effective surface passivation compared to SPTP-MeTPA, which has a nonplanar spatial arrangement. As a result, the champion device based on SPCF-MeTPA achieves efficiencies of 26.35% (certified 25.75%) and 24.55% for aperture areas of 0.07 and 1.01 cm2, respectively. Additionally, these devices demonstrate exceptional long-term stability, further highlighting the potential of SPCF-MeTPA as a high-performance HTM.

Mercapto-functionalized scaffold improves perovskite buried interfaces for tandem photovoltaics

Tandem photovoltaics hold great potential to surpass the efficiency limit of single-junction solar cells. Detrimental structural defects and chemical reactions at buried interfaces of subcells considerably impede the performance of integrated tandems. Here, we devise a mercapto-functionalized mesoporous silica layer as a superstructure at the buried interface to modulate the crystallisation, eliminate nanovoids, passivate defects, and suppress the oxidation of Sn(II) in the tin-lead perovskite films, contributing substantially to reduce charge carrier losses and improve stability in positive-intrinsic-negative structured devices. Consequently, the tin-lead perovskite single-junction cells show efficiency values of up to 23.7% with the best open-circuit voltage of 0.89 V. With the enhanced subcells, our double-junction tandems show efficiency values of 29.6% (certified 29.5% and steady-state 28.7%) and 24.7% on solar cells and 11.3 cm2 mini-modules, respectively. Encapsulated tandems maintain 90% of initial efficiency after 445 h of maximum power point tracking under simulated 1-sun illumination.

Metalized Porphyrin-Based COFs for Conductive Porous Layers in Perovskite Solar Cells to Enhance Electron Injection, Defect Passivation, and Lead-Protection

In perovskite solar cells (PSCs), the introduction of an intermediate layer to bridge the transport and photoactive layers has become a key strategy for enhancing carrier extraction efficiency. However, traditional approaches are often limited by the seesaw effect, making it challenging to achieve an optimal balance between electron transport and defect passivation. In this study, we employed a Cu2+-loaded metalized porphyrin-based covalent organic framework (Cu-Por-COF) as a conductive porous layer (CPL) at the perovskite bottom interface. Experimental results showed that a Cu-Por-COF coverage of 19% significantly enhanced electron transport and effectively suppressed long-distance electron diffusion. Moreover, the carefully designed Cu-Por-COF provided abundant active sites, which improved the film-forming quality of the perovskite layer, thereby facilitating the beneficial synergy of electron injection and defect passivation. The n-i-p type devices achieved a power conversion efficiency (PCE) of 25.41% (0.09 cm2) and 21.99% (1.01 cm2). Using Cu-Por-COF to stabilize the perovskite crystal structure, the unencapsulated devices retained over 81% of its initial efficiency after 2000 h. Additionally, Cu-Por-COF effectively chelated lead ions and thus enhanced the environmental sustainability of PSCs.

Buried interfacial passivation by a multifunctional molecular bridge for blade-coating perovskite solar cells

A multifunctional molecular bridge was introduced to passivate the buried interface of doctor-bladed p-i-n perovskite solar cells. By incorporating specific functional groups into the hole transport layer, this approach strengthens the buried interface bonding, improves crystallinity, and reduces defect density, resulting in enhanced stability and reproducibility across various substrates.

Perovskite Solar Cells and Light Emitting Diodes: Materials Chemistry, Device Physics and Relationship

Solution-processed perovskite solar cells (PSCs) and perovskite light emitting diodes (PeLEDs) represent promising next-generation optoelectronic technologies. This Review summarizes recent advancements in the application of metal halide perovskite materials for PSC and PeLED devices to address the efficiency, stability and scalability issues. Emphasis is placed on material chemistry strategies used to control and engineer the composition, deposition process, interface and micro-nanostructure in solution-processed perovskite films, leading to high-quality crystalline thin films for optimal device performance. Furthermore, we retrospectively compare the device physics of PSCs and PeLEDs, their working principles and their energy loss mechanisms, examining the similarities and differences between the two types of devices. The reciprocity relationship suggests that a great PSC should also be a great PeLED, motivating the search for interconverting photoelectric bifunctional devices with maximum radiative recombination and negligible non-radiative recombination. Specific requirements of PSCs and PeLEDs in terms of bandgap, thickness, band alignment and charge transport to achieve this target are discussed in detail. Further challenges and issues are also illustrated, together with prospects for future development. Understanding these fundamentals, embracing recent breakthroughs and exploring future prospects pave the way toward the rational design and development of high-performance PSC and PeLED devices.

Multidimensional Modulation via Tailored Covalent Organic Frameworks Enables Stable Inverted Perovskite Solar Cells with 26.21% Efficiency

Despite the remarkable advancements in inverted perovskite solar cells, their commercialization remains hindered by critical bottlenecks in efficiency and stability stemming from inadequate crystallization and unfavorable interfacial states. Herein, for the first time, a judiciously designed hydrazine-linked covalent organic framework (COF) with long alkane phosphate branch chains, named 12-SD-COF, is synthesized and integrated into the perovskite precursor to achieve multidimensional regulation of crystallization, defect states, and charge separation synergistically. It is found that the 12-SD-COF featuring periodic pores, large planar structure, and abundant binding groups is extruded from the precursor solution onto the buried interface, surface, and grain boundaries, facilitating oriented crystallization while eliminating defects of perovskites, thereby yielding high-quality crystals with suppressed non-radiative recombination. Simultaneously, the interfacial charge separation is synergistically facilitated by the p-type doping-optimized energy level alignment and the induced intramolecular electric field, ultimately achieving an exceptional power conversion efficiency (PCE) of 26.21%, the highest yet reported for COF-modified. Impressively, the non-encapsulated resultant device delivers greatly improved stabilities, with maintaining over 92% of initial PCE after being aged under 85 °C continuous heating stress for 800 h, 1000 h in 50±3% relative humidity air, and 1200 h under continuous 1-sun illumination, respectively.

Heat-Triggered Dynamic Self-Healing Framework for Variable-Temperature Stable Perovskite Solar Cells

Metal halide perovskite solar cells (PSCs) are promising as the next-generation photovoltaic technology. However, the inferior stability under various temperatures remains a significant obstacle to commercialization. Here, a heat-triggered dynamic self-healing framework (HDSF) is implemented to repair defects at grain boundaries caused by thermal variability, enhancing PSCs' temperature stability. HDSF, distributed at the grain boundaries and surface of the perovskite film, stabilizes the perovskite lattice and releases the perovskite crystal stress through the dynamic exchange reaction of sulfide bonds. The resultant PSCs achieved a power-conversion efficiency (PCE) of 26.32% (certified 25.84%) with elevated temperature stability, retaining 88.7% of the initial PCE after 1000 h at 85 °C. In a variable temperature cycling test (between -40 and 80 °C), the HDSF-treated device retained 87.6% of its initial PCE at -40 °C and 92.6% at 80 °C after 160 thermal cycles. This heat-triggered dynamic self-healing strategy could significantly enhance the reliability of PSCs in application scenarios.

Chelated tin halide perovskite for near-infrared neuromorphic imaging array enabling object recognition and motion perception

Neuromorphic imaging arrays integrate sensing, memory, and processing for efficient spatiotemporal fusion, enabling intelligent object and motion recognition in autonomous and surveillance systems. Halide perovskites offer potential for neuromorphic imaging by regulating photogenerated ions and charges, but lead toxicity and limited response range remain key limitations. Here, we present lead-free non-toxic formamidinium tin triiodide perovskites functionalized with bio-friendly quercetin molecules via a multi-site chelate strategy, achieving favorable near-infrared response and optoelectronic properties. Leveraging a non-equilibrium photogenerated carrier strategy, the formamidinium tin triiodide-quercetin based near-infrared optoelectronic synapses exhibit key synaptic features for practical applications, including quasi-linear time-dependent photocurrent generation, prolonged photocurrent decay, high stability, and low energy consumption. Ultimately, a 12 × 12 real-time neuromorphic near-infrared imaging array is constructed on thin-film transistor backplanes, enabling hardware-level spatiotemporal fusion for robust object recognition and motion perception in complex environments for autonomous and surveillance systems.

Reconstruction of the Buried Interface of Triple-Halide Wide-Bandgap Perovskite for All-Perovskite Tandems

All-perovskite tandem solar cells (TSCs) paired by wide-bandgap (WBG) perovskites with narrow-bandgap perovskites holds the potential to overcome the Shockley-Queisser limitation. However, the severe phase segregation and non-radiative recombination of WBG perovskite put on a shadow for their power conversion efficiency and stability. Here, an interfacial engineering strategy is introduced into the triple-halide WBG perovskite. Potassium trifluoromethanesulfonate (TfOK) is utilized to reconstruct the buried interface of the triple-halide WBG perovskite. The distribution of (chlorine) Cl- changes from perovskite bulk toward the buried interface due to the TfOK addition. Therefore, a wider bandgap perovskite thin layer is formed at buried layer, which can form a graded heterojunction with bulk WBG perovskite to improve carrier separation and transfer. Meanwhile, the (potassium) K+ of TfOK diffuses into WBG perovskite bulk to suppress halide phase segregation. Consequently, the 1.78 eV WBG PSCs deliver an impressive power conversion efficiency of 20.47% and an extremely high fill factor over 85%. Furthermore, the resultant two-terminal all-perovskite TSCs achieves a champion efficiency of 28.30%. This strategy provides a unique avenue to improve performance and photostability of WBG PSCs, a new function of Cl- in triple-halide is illustrated.

Grains > 2 µm with Regulating Grain Boundaries for Efficient Wide-Bandgap Perovskite and All-Perovskite Tandem Solar Cells

Tandem perovskite solar cells represent a significant avenue for the future development of perovskite photovoltaics. Despite their promise, wide-bandgap perovskites, essential for constructing efficient tandem structures, have encountered formidable challenges. Notably, the high bromine content (>40%) in these 1.78 eV bandgap perovskites triggers rapid crystallization, complicating the control of grain boundary growth and leading to films with smaller grain sizes and higher defect density than those with narrower bandgaps. To address this, potassium tetrakis(pentafluorophenyl)borate molecules are incorporated into the antisolvent, employing a crystallographic orientation-tailored strategy to optimize grain boundary growth, thereby achieving wide-bandgap perovskite films with grains exceeding 2 µm and effectively eliminating surplus lead halide and defects at the grain boundaries. As a result, remarkable efficiency is achieved in single-junction wide-bandgap perovskite devices, with a power conversion efficiency (PCE) of 20.7%, and in all-perovskite tandem devices, with a two-terminal PCE of 28.3% and a four-terminal PCE of 29.1%, which all rank among the highest reported values in the literature. Moreover, the stability of these devices has been markedly improved. These findings offer a novel perspective for driving further advancements in the perovskite solar cell domain.

Role of self-assembled molecules in halide perovskite optoelectronics: an atomic-scale perspective

Despite significant advancements in the study of metal halide perovskites worldwide, the large-scale industrialization of related optoelectronic devices faces ongoing challenges related to efficiency, long-term stability, and environmental and human toxicity. Self-assembled molecules (SAMs) have recently emerged as crucial strategies for enhancing device performance and stability, particularly by mitigating interface-related challenges. This review provides a comprehensive examination of the multifaceted roles of SAMs in enhancing the performance and stability of perovskite optoelectronic devices. We begin by introducing the evolution of SAMs, their unique physicochemical properties and implemented applications in optoelectronic devices. Subsequently, we delve into the diverse beneficial effects of SAMs in perovskite devices and elucidate the underlying atomic-scale mechanisms responsible for these performance enhancements. Finally, we critically analyze the current challenges associated with the rational design and implementation of SAMs in perovskite devices and conclude by outlining promising future research directions.

In Situ Construction of Multi-Functional Polymer Network Toward Durable Perovskite Solar Cells

Enhancing the crystalline quality of perovskite thin films and stabilizing their internal grain boundaries are essential in guaranteeing the extended longevity of perovskite solar cells. Herein, an in situ polymerization strategy is presented to produce weak chemical bond networks in perovskite films. The introduction of acrylamide monomer into the perovskite precursor solution facilitates the rearrangement of [PbI6]4- octahedra, resulting in a significant enhancement of the crystal quality of the perovskite films. With the presence of C═C bonds, the in situ polymerization of acrylamide at grain boundaries can form polymer networks, which can efficiently passivate the detrimental defects associated with grain boundaries. The perovskite solar cells with an impressive power conversion efficiency (PCE) of 26.05% (certified at 25.06%) are achieved, combined with highly improved operational stability with T98 = 2034 h. As expected, large-area module based on this strategy achieved an impressive PCE of 23.02% with an active area of 14 cm2.

Spin effects in metal halide perovskite semiconductors

Metal halide perovskite semiconductors (MHSs) are emerging as potential candidates for opto-spintronic applications due to their strong spin-orbit coupling, favorable light emission characteristics and highly tunable structural symmetry. Compared to the significant advancements in the optoelectronic applications of MHSs, the exploration and control of spin-related phenomena remain in their early stages. In this minireview, we provide an overview of the various spin effects observed both in achiral and chiral MHSs, emphasizing their potential for controlling interconversion between spin, charge and light. We specifically highlight the spin selective properties of chiral MHSs through the chirality-induced spin selectivity (CISS) phenomena, which enable innovative functionalities in devices such as spin-valves, spin-polarized light-emitting diodes, and polarized photodetectors. Furthermore, we discuss the prospects of MHSs as spintronic semiconductors and their future development in terms of material design, device architecture and stability.

Multifunctional Ruthenium Dye Assists PTAA-Based Inverted Perovskite Solar Cells

In inverted perovskite solar cells (PSCs), although PTAA (poly[bis(4-phenyl)(2,4,6-trimethylphenyl)amine]) has been extensively utilized as a hole transport material, its inherent poor wettability and energy level misalignment with perovskite have become critical issues, limiting the improvement of power conversion efficiency (PCE) and long-term stability of PSCs. For overcoming these challenges, our study employs a typical multifunctional dye molecule, N719 (ditetrabutylammonium cis-bis(isothiocyanato)bis(2,2'-bipyridyl-4,4'-dicarboxylato) ruthenium(II)), to modify PTAA. Thanks to the incorporation of hydrophilic functional groups in N719, the wettability of the PTAA/N719 film is improved, which in turn boosts the crystallinity of the perovskite film. Additionally, the rich functional groups in N719 can interact with uncoordinated Pb2+, thereby reducing the defect state density in perovskite. Furthermore, the improved energy level alignment enhances hole extraction capability. Ultimately, the champion device fabricated based on the PTAA/N719 film had a PCE as high as 23.83%, showing a significant improvement compared to the PCE of the unmodified device (20.80%). Moreover, the N719-modified devices exhibited superior long-term stability, with the unencapsulated devices maintaining a PCE greater than 81% of the initial value after being stored for 1500 h under ambient conditions at room temperature. This study demonstrates that dyes represent a promising material for enhancing the performance of inverted PSCs.

Modulating competitive adsorption of hybrid self-assembled molecules for efficient wide-bandgap perovskite solar cells and tandems

The employment of self-assembled molecular hybrid could improve buried interface in perovskite solar cells (PSCs). However, the interplay among hybrid self-assembled monolayers (SAMs) during the deposition process has not been well-studied. Herein, we study the interaction between co-adsorbents and commonly used SAM material, [4-(3,6-dimethyl-9H-carbazol-9-yl)butyl]phosphonic acid (Me-4PACz) for wide-bandgap (WBG) PSCs. It is found that the co-adsorbent, 6-aminohexane-1-sulfonic acid (SA) tends to fill the uncovered sites without interference with Me-4PACz, ensuring the formation of a dense hole selective layer. Moreover, the use of SA/Me-4PACz mixed SAMs could effectively reduce the interfacial non-radiative recombination loss, optimize the energy alignment at the buried interface and regulate the crystallization of WBG perovskite. As a result, the 1.77 eV WBG PSCs deliver a power conversion efficiency (PCE) of 20.67% (20.21% certified) and an impressive open-circuit voltage (VOC) of 1.332 V (1.313 V certified). By combining with a 1.26 eV narrow-bandgap (NBG) PSC, we further fabricate 2-terminal all-perovskite tandem solar cells (TSCs) with a PCE of 28.94% (28.78% certified) for 0.087 cm2 and 23.92% for mini-module with an aperture area of 11.3 cm2.

Restrain Phase Segregation by In Situ Buried Prenucleation for Efficient and Stable Wide-Band Gap Perovskite Cells

The phase segregation of wide-band gap perovskite solar cells (PSCs) typically originates from defect centers and strain induced by nonstoichiometric compounds. In this study, we have discovered an excess of PbI2 at the buried interface in inverted wide-band gap PSCs. To address this issue, RbI is introduced to interact with the excessive PbI2, thereby in situ forming a layer of inorganic perovskite RbPbI3. The presence of RbPbI3 as prenucleation centers facilitates intimate contact and enhances crystallinity of the wide-band gap perovskite, thereby alleviating lattice strain and reducing nonradiative recombination centers. Consequently, ion migration is suppressed, and phase segregation at the buried interface is inhibited. After the addition of RbI, the power conversion efficiency (PCE) of the wide-band gap semitransparent device is increased from 17.96 to 19.5%, and the bifacial factor is 83.4%. Furthermore, after continuous illumination at an intensity equivalent to AM 1.5 G for 1000 h, the device based on RbI retains approximately 81.71% of its initial PCE.

Anchorable Polymers Enabling Ultra-Thin and Robust Hole-Transporting Layers for High-Efficiency Inverted Perovskite Solar Cells

Currently, the development of polymeric hole-transporting materials (HTMs) lags behind that of small-molecule HTMs in inverted perovskite solar cells (PSCs). A critical challenge is that conventional polymeric HTMs are incapable of forming ultra-thin and conformal coatings like self-assembly monolayers (SAMs), especially for substrates with rough surface morphology. Herein, we address this challenge by designing anchorable polymeric HTMs (CP1 to CP5). Specifically, coordinative pyridyl groups are introduced as side-chains on poly-triarylamine (PTAA) backbone with varied contents by copolymerization method, resulting in chemical interactions between polymeric HTMs and substrates. The strong interaction allows them to be processed into ultra-thin, uniform, and robust hole-transporting layers through employing low-concentration solutions (0.1 mg mL-1, vs. 2.0-5.0 mg mL-1 for conventional PTAA), greatly decreasing charge transport losses. Moreover, upon systematically tuning the pyridyl substitution ratio, the energy levels, surface wetting, solution processability, and defect passivation capability of such anchorable HTMs are simultaneously optimized. Based on the optimal CP4, we achieved highly efficient inverted PSCs with power conversion efficiencies (PCEs) up to 26.21 %, which is on par with state-of-the-art SAM-based inverted PSCs. Furthermore, these devices exhibit enhanced stabilities under repeated current-voltage scans and reverse bias ageing compared with SAM-based devices.

3,6-Bis(methylthio)-9H-carbazole Based Self-Assembled Monolayer for Highly Efficient and Stable Inverted Perovskite Solar Cells

The photovoltaic performance of inverted perovskite solar cells (PSCs) relies on effectively managing the interface between the hole extraction layer and the light-absorbing perovskite layer. In this study, we have synthesised (4-(3,6-bis(methylthio)-9H-carbazol-9-yl)butyl)phosphonic acid (MeS-4PACz), which forms a self-assembled monolayer (SAM) on the fluorine-doped tin oxide (FTO) electrode. The molecule's methylthio substituents generate a favourable interfacial dipole moment and interact with the perovskite layer. This interaction results in well-aligned energy levels among the FTO/SAM/perovskite layers, promoting efficient hole extraction and significantly reducing carrier recombination losses. Additionally, the methylthio groups passivate iodide vacancies and interact with Pb2+ ions of the perovskite, reducing defect-induced trap states and enhancing the crystalline growth of the perovskite layer. Consequently, inverted PSCs incorporating MeS-4PACz achieve a power conversion efficiency of 25.13 %, along with outstanding photostability.

Dynamic Passivation of Perovskite Films via Gradual Additive Release for Enhanced Solar Cell Efficiency

Modifying perovskites with functional additives has proven effective in refining the crystallization process and passivating the defects of perovskite films, thereby ensuring high photovoltaic efficiencies. However, conventional methods that involve pre-mixing additives into the precursor solution often face challenges due to discrepancies in the spatial distribution of slow-diffused additives relative to dynamically formed defect sites, resulting in limited passivation effectiveness. To address this issue, this study innovatively proposes a dynamic passivation strategy that utilizes a pre-passivator to gradually release active additives during the thermal crystallization process of perovskite films. By leveraging the principle of energy minimization, these timely-released additives can interact precisely and selectively with the high-energy defect sites generated during crystallization, thus facilitating efficient additive utilization and in situ real-time defect passivation. Through analysis of crystallization kinetics and carrier dynamic, it is demonstrated that this dynamic passivation approach significantly improves film quality and prolongs carrier lifetime, outperforming traditional pre-mixing tactics. Consequently, the final perovskite solar cell achieves an impressive solar conversion efficiency of 25.33 %, along with exceptional stability. This work provides strong support of tailored additive strategies aimed at further enhancing the efficiency of perovskite solar cells and their subsequent commercial applications.

In situ Polymerization Induced Seed-Root Anchoring Structure for Enhancing Stability and Efficiency in Perovskite Solar Modules

The escape of organic cations over time from defective perovskite interface leads to non-stoichiometric terminals, significantly affecting the stability of perovskite solar cells (PSCs). How to stabilize the interface composition under environmental stress remains a grand challenge. To address this issue, we utilize thiol-functionalized particles as a "seed" and conduct in situ polymerization of 2,2,3,4,4,4-hexafluorobutyl methacrylate (HFMA) as a "root" at the bottom of the perovskite layer. In this process, the thiol group acts as the initiation site for the polymerization of HFMA, while the fluorine groups in HFMA firmly anchor the organic cations of the perovskite through multiple hydrogen bonds. This strategy resembles how seeds take root in soil to prevent soil erosion. This bionic seed-rooting structure effectively stabilizes the stoichiometry of the perovskite, thus suppressing the escape of organic cations. As a result, the perovskite films with seed-rooting structures exhibit enhanced stability under harsh vacuum thermal conditions (150 °C, <10 Pa). The resulting PCS achieves an efficiency of 25.64 % and a 22.4 cm2 module efficiency of 22.61 %. After 1300 hours of 1-sun illumination at 85 % relative humidity and 65 °C (ISOS-L-3 protocol), the perovskite solar module maintains 90 % of its initial efficiency.

Reactive Plasma Deposition of ITO as an Efficient Buffer Layer for Inverted Perovskite Solar Cells

In this study, the potential of reactive plasma deposition (RPD) is demonstrated for fabricating indium tin oxide (ITO) as an efficient buffer layer in inverted wide-bandgap perovskite solar cells (PSCs). This method results in a certified efficiency of 21.33% for wide-bandgap PSCs, demonstrating superior thermal stability and operational stability. The optimized devices achieve an impressive open-circuit voltage (VOC) of 1.252 V with a bandgap of 1.67 eV, resulting in a remarkably low voltage deficit of 0.418 V, attributed to improved electron extraction, reduced interface defects, and suppressed surface recombination. The cells maintain over 90% of their initial efficiency after 1023 h of thermal aging at 88 °C. Furthermore, by integrating a highly efficient semi-transparent PSC with a CIGS bottom cell, a four-terminal tandem configuration is achieved with a total efficiency of 29.03%, representing one of the most efficient perovskite/CIGS tandem solar cells reported to date. This study provides valuable insights into the potential of RPD for improving the performance and scalability of inverted wide-bandgap PSCs.

A Chain Entanglement Gelled SnO₂ Electron Transport Layer for Enhanced Perovskite Solar Cell Performance and Effective Lead Capture

SnO₂ is a widely used electron transport layer (ETL) material in perovskite solar cells (PSCs), and its design and optimization are essential for achieving efficient and stable PSCs. In this study, the in situ formation of a chain entanglement gel polymer electrolyte is reported in an aqueous phase, integrated with SnO₂ as the ETL. Based on the self-polymerization of 3-[[2-(methacryloyloxy)ethyl]dimethylammonium]propane-1-sulfonic acid (DAES) in an aqueous environment, combining the catalytic effect of LiCl (as a Lewis acid) with the salting-out effect, and the introduction of polyvinylpyrrolidone (PVP) as the other polymer chain, a chain entanglement gelled SnO2 (G-SnO2) structure is successfully constructed with a wide range of functions. The PDEAS-PVP chain entanglement gel achieves passivation and Pb2⁺ capture through chemical chelation mechanisms is explored. The results demonstrated that the all-in-air prepared PSC based on G-SnO2 exhibited an excellent power conversion efficiency (PCE) of 24.77% and retained 83.3% of their initial efficiency after 2100 h of air exposure. Additionally, the PDEAS-PVP exposes more C═O and S═O active sites, significantly enhanced the lead absorption capability of the PSCs.

Biomass Derived Self-Doped Carbon Nanosheets Enable Robust Hole Transport Layers with Ion Buffer for Perovskite Solar Cells

The diffusion of iodine species and lead leakage during device degradation represent the main obstacles restricting the commercial application of perovskite solar cells (PSCs). Cobalt loaded ultrathin carbon nanosheets (Co(III)-CNS) derived from biomass are prepared as ion buffer material to construct robust hole transport layers (HTLs). The carbon nanosheets containing trivalent cobalt ions can facilitate the oxidation of the hole transport material while preserving the structural integrity and electrical properties of HTLs under thermal stress, thereby ensuring efficient carrier transport. The two-dimensional ultrathin graphitized lamellar structure of Co(III)-CNS is conducive to alleviate the corrosive effects of the outward diffusion of iodine species on HTLs and silver electrodes, while avoiding irreversible degradation of PSCs. With the improvement of HTL composition and the related interfaces, Co(III)-CNS doped devices can maintain intact device structure under thermal stress and remain above 80 % of the original power conversion efficiency (PCE) after thermal aging at 85 °C for 720 h. Notably, the chemical interactions between heteroatoms of self-doped carbon nanosheets and the mobile lead ions can effectively alleviate lead leakage and avoid the potential impacts of device degradation on ecosystem. Ultimately, the Co(III)-CNS doped PSCs with enhanced thermal stability exhibit a champion PCE of 22.32 %.

Metal-halide porous framework superlattices

The construction of superlattices with a spatial modulation of chemical compositions allows for the creation of artificial materials with tailorable periodic potential landscapes and tunable electronic and optical properties1-5. Conventional semiconductor superlattices with designable potential modulation in one dimension has enabled high-electron-mobility transistors and quantum-cascade lasers. More recently, a diverse set of superlattices has been constructed through self-assembly or guided assembly of multiscale building units, including zero-dimensional nanoclusters and nanoparticles6,7, one-dimensional nanorods and nanowires8,9, two-dimensional nanolayers and nanosheets10-13, and hybrid two-dimensional molecular assemblies14-17. These self-assembled superlattices feature periodic structural modulation in two or three dimensions, but often lack atomic precision owing to the inevitable structural disorder at the interfaces between the constituent units. Here we report a one-pot synthesis of multi-dimensional single-crystalline superlattices consisting of periodic arrangement of zero-, one- and two-dimensional building units. By exploiting zirconium (IV) metal-organic frameworks as host templates for directed nucleation and precise growth of metal-halide sublattices through a coordination-assisted assembly strategy, we synthesize a family of single-crystalline porous superlattices. Single-crystal X-ray crystallography and high-resolution transmission electron microscopy clearly resolve the high-order superlattice structure with deterministic atomic coordinates. Further treatment with selected amine molecules produces perovskite-like superlattices with highly tunable photoluminescence and chiroptical properties. Our study creates a platform of high-order single-crystalline porous superlattices, opening opportunities to tailor the electronic, optical and quantum properties beyond the reach of conventional crystalline solids.

Interfacial Work Function Modulation of Wide Bandgap Perovskite Solar Cell for Efficient Perovskite/CIGS Tandem Solar Cell

Wide-bandgap perovskite solar cells (PVSCs), a promising top-cell candidate for high-performance tandem solar cells, often suffer from larger open-circuit voltage (VOC) deficits as the bandgap increases. Surface passivation is a common strategy to mitigate these VOC deficits. However, understanding the mechanisms underlying the differences in passivation effects among various types of molecules remains limited, which is crucial for developing universal interface passivation strategies and guiding the design of passivation molecules. This study compares the passivation effects of phenethylammonium iodide (PEAI) and piperazine iodine (PI) on VOC in wide-bandgap PVSCs with a 1.66 eV bandgap. Results show that PI significantly enhances VOC, whereas PEAI does not. This improvement is attributed to increased built-in voltage (Vbi) in PI-treated PVSCs, stemming from a lower work function, which enhances carrier selectivity at the contact interfaces. The champion power conversion efficiency of the PVSCs is 21.47%, with a VOC of 1.23 V and a VOC loss of 0.43 V. The strategy is also effective for PVSCs with bandgaps of 1.56 and 1.81 eV. By layering semi-transparent perovskite top cells onto copper indium gallium selenide (CIGS) bottom cells, a PCE of 26.36% is achieved in perovskite/CIGS 4-terminal tandem solar cells.

Revealing and Inhibiting the Facet-related Ion Migration for Efficient and Stable Perovskite Solar Cells

Ion migration is a major issue hindering the long-term stability of perovskite solar cells (PSCs). As an intrinsic characteristic of metal halide perovskite materials, ion migration is closely related to the atomic arrangement and coordination, which are the basic characteristic differences among various facets. Herein, we report the facet-related ion migration, and then achieve the inhibition of ion migration in perovskite through finely modulating the facet orientation. We show that the (100) facet is substantially more vulnerable to cationic migration than the (111) facet. The main reason for this difference in migration is that the cationic migration route in the (111) facet deviates from that in the (100) facet, which increases the active migration energy and weakens the contribution from the electric field during operation. We prepare a (111)-dominated perovskite film by incorporating a facile and green addition of water (H2O) into the antisolvent, further achieving a power conversion efficiency (PCE) of 26.0 % (25.4 % certification) on regular planar PSCs and 25.8 % on inverted PSCs. Moreover, the unencapsulated PSCs can maintain 95 % of their initial PCE after 3500-hours operation under simulated AM1.5 illumination at the maximum power point.

Enhancing Charge-Emitting Shallow Traps in Metal Halide Perovskites by >100 Times by Surface Strain

The low density of deep trapping defects in metal halide perovskites (MHPs) is essential for high-performance optoelectronic devices. Shallow traps in MHPs are speculated to enhance charges recombination lifetime. However, it is unknown about the shallow trap chemical nature and distribution, and impact on solar cell operation. Herein, we report that shallow traps are much richer in MHPs than traditional semiconductors. Their density can be enhanced by >100 times through local surface strain, indicating shallow traps mainly located at the surface. The surface strain is introduced by anchoring two-amine-terminated molecules onto formamidinium cations, and the shallow traps are formed by the band edge downshifting toward defect levels. The high-density shallow traps temporarily hold one type of charges and increased concentration of the other type of free carrier in working solar cells by keeping photogenerated charges from bimolecular recombination, resulting in reduced open circuit voltage loss to 317 mV.

Cyclic Multi-Site Chelation for Efficient and Stable Inverted Perovskite Solar Cells

Trap-assisted non-radiative recombination losses and moisture-induced degradation significantly impede the development of highly efficient and stable inverted (p-i-n) perovskite solar cells (PSCs), which require high-quality perovskite bulk. In this research, we mitigate these challenges by integrating thermally stable perovskite layers with Lewis base covalent organic frameworks (COFs). The ordered pore structure and surface binding groups of COFs facilitate cyclic, multi-site chelation with undercoordinated lead ions, enhancing the perovskite quality across both its bulk and grain boundaries. This process not only reduces defects but also promotes improved energy alignment through n-type doping at the surface. The inclusion of COF dopants in p-i-n devices achieves power conversion efficiencies (PCEs) of 25.64 % (certified 24.94 %) for a 0.0748-cm2 device and 23.49 % for a 1-cm2 device. Remarkably, these devices retain 81 % of their initial PCE after 978 hours of accelerated aging at 85°C, demonstrating remarkable durability. Additionally, COF-doped devices demonstrate excellent stability under illumination and in moist conditions, even without encapsulation.

Small-Molecule Hole Transport Materials for >26% Efficient Inverted Perovskite Solar Cells

Chemically modifiable small-molecule hole transport materials (HTMs) hold promise for achieving efficient and scalable perovskite solar cells (PSCs). Compared to emerging self-assembled monolayers, small-molecule HTMs are more reliable in terms of large-area deposition and long-term operational stability. However, current small-molecule HTMs in inverted PSCs lack efficient molecular designs that balance both the charge transport capability and interface compatibility, resulting in a long-standing stagnation of power conversion efficiency (PCE) below 24.5%. Here, we report the comprehensive design of HTMs' backbone and functional groups, which optimizes a simple planar linear molecular backbone with a high mobility exceeding 7.1 × 10-4 cm2 V-1 S-1 and enhances its interface anchoring capability. Owing to the improved surface properties and anchoring effects, the tailored HTMs enhance the interface contact at the HTM/perovskite heterojunction, minimizing nonradiative recombination and transport loss and leading to a high fill factor of 86.1%. Our work has overcome the persistent efficiency bottleneck for small-molecule HTMs, particularly for large-area devices. Consequently, the resultant PSCs exhibit PCEs of 26.1% (25.7% certified) for a 0.068 cm2 device and 24.7% (24.4% certified) for a 1.008 cm2 device, representing the highest PCE for small-molecule HTMs in inverted PSCs.

Spontaneous bifacial capping of perovskite film for efficient and mechanically stable flexible solar cell

Flexible perovskite solar cells (F-PSCs) are appealing for their flexibility and high power-to-weight ratios. However, the fragile grain boundaries (GBs) in perovskite films can lead to stress and strain cracks under bending conditions, limiting the performance and stability of F-PSCs. Herein, we show that the perovskite film can facilely achieve in situ bifacial capping via introducing 4-(methoxy)benzylamine hydrobromide (MeOBABr) as the precursor additive. The spontaneously formed MeOBABr capping layers flatten the grain boundary grooves (GBGs), enable the release of the mechanical stress at the GBs during bending, rendering enhanced film robustness. They also contribute to the reduction of the residual strain and the passivation of the surface defects of the perovskite film. Besides, the molecular polarity of MeOBABr can result in surface band bending of the perovskite that favors the interfacial charge extraction. The corresponding inverted F-PSCs based on nickel oxide (NiOx)/poly(triaryl amine) (PTAA) hole transport bilayer reach a 23.7% power conversion efficiency (PCE) (22.9% certified) under AM 1.5 G illumination and a 42.46% PCE under 1000 lux indoor light illumination. Meanwhile, a robust bending durability of the device is also achieved.

Highly stable perovskite solar cells with 0.30 voltage deficit enabled by a multi-functional asynchronous cross-linking

The primary challenge in commercializing perovskite solar cells (PSCs) mainly stems from fragile and moisture-sensitive nature of halide perovskite materials. In this study, we propose an asynchronous cross-linking strategy. A multifunctional cross-linking initiator, divinyl sulfone (DVS), is firstly pre-embedded into perovskite precursor solutions. DVS, also as a special co-solvent, facilitates intermediate-dominated perovskite crystallization manipulation, favouring formamidine-DVS based solvate transition. Subsequently, DVS-embedded perovskite as-cast films are post-treated with a nucleophilic reagent, glycerinum, to trigger controllably three-dimensional co-polymerization. The resulting cross-linking scaffold provides enhanced water-resistance, releases residual tensile strain, and suppresses deep-level defects. We achieve a maximum efficiency over 25% (certified 24.6%) and a maximum VOC of 1.229 V, corresponding to mere 0.30 V deficit, reaching 97.5% of the theoretical limit, which is the highest reported in all perovskite systems. This strategy is generally applicable with enhanced efficiencies approaching 26%. All-around protection significantly improves PSC's operational longevity and thermal endurance.

Surface Planarization-Epitaxial Growth Enables Uniform 2D/3D Heterojunctions for Efficient and Stable Perovskite Solar Modules

Two-dimensional/three-dimensional (2D/3D) halide perovskite heterojunctions are widely used to improve the efficiency and stability of perovskite solar cells. However, interfacial defects between the 2D and 3D perovskites and the poor coverage of the 2D capping layer still hinder long-term stability and homogeneous charge extraction. Herein, a surface planarization strategy on 3D perovskite is developed that enables an epitaxial growth of uniform 2D/3D perovskite heterojunction via a vapor-assisted process. The homogeneous charge extraction and suppression of interfacial nonradiative recombination is achieved by forming a uniform 2D/3D interface. As a result, a stabilized power output efficiency of 25.97% is achieved by using a 3D perovskite composition with a bandgap of 1.55 eV. To demonstrate the universality of the strategy applied for different perovskites, the champion device based on a 1.57 eV bandgap 3D perovskite results in an efficiency of 25.31% with a record fill factor of 87.6%. Additionally, perovskite solar modules achieve a designated area (24.04 cm2) certified efficiency of 20.75% with a high fill factor of 80.0%. Importantly, the encapsulated uniform 2D/3D modules retain 96.9% of the initial efficiency after 1246 h operational tracking under 65 °C (ISOS-L-3 protocol) and 91.1% after 862 h under the ISOS-O-1 protocol.

Minimizing Voltage Deficit in Perovskite Indoor Photovoltaics by Interfacial Engineering

Metal halide perovskites with bandgap of ≈1.8 eV are competitive candidates for indoor photovoltaic (IPV) devices, owing to their superior photovoltaic properties and ideal absorption spectra matched to most indoor light sources. However, these perovskite IPVs suffer from severe trap induced non-radiative recombination, resulting in large open-circuit voltage (VOC) losses, particularly under low light intensity. Herein, an effective approach is developed to minimizing trap density by modifying the buried interface of perovskite layer with bifunctional molecular 2-(4-Fluorophenyl)ethylamine Hydrobromide (F-PEABr). The benzene ring of F-PEABr molecules can firmly anchor at the hole transporting layer by π-π stacking interaction, and the other ends can passivate the defects on the buried interface of perovskite layer. Based on that, the F-PEABr modified perovskite IPVs achieved power conversion efficiency (PCE) of 42.3% with a remarkable VOC of 1.13 V under 1000 lux illumination from a 4000 K LED lamp. Finally, perovskite IPV mini-modules with area of 10.40 cm2 are demonstrated with a PCE of 35.2%. This interface modification strategy paves the way for crafting high-performance perovskite IPVs, holding great potential for self-powered internet of things applications.

Reconstruction of Hole Transport Layer via Co-Self-Assembled Molecules for High-Performance Inverted Perovskite Solar Cells

Adjusting the hole transport layer (HTL) to optimize its interface with perovskite is crucial for minimizing interface recombination, enhancing carrier extraction, and achieving efficient and stable inverted perovskite solar cells (PSCs). However, as a commonly used HTL, the self-assemble layer (SAM) of [2-(3,6-dimethoxy-9H-carbazol-9-yl)ethyl] phosphonic acid (MeO-2PACz) tends to form clusters and micelles during the deposition process, leading to inadequate coverage of the ITO substrate. Here, a Co-SAM strategy is employed by incorporating 4-mercaptobenzoic acid (SBA) and 4-trifluoromethyl benzoic acid (TBA) as additives into MeO-2PACz to fabricate a Co-SAM-based HTL. The introduced additive can interact with MeO-2PACz, facilitating cluster dispersion and thereby enabling better deposition on ITO for improved HTL coverage. Moreover, Co-SAM exhibits superior energy level alignment with perovskite to enhance interfacial contact and improve carrier extraction efficiency as well as promote growth of bottom perovskite grains. As a result, an impressive increase of the power conversion efficiency (PCE) from 21.34% to 23.31% is achieved in the inverted device based on the Co-SAM HTL of MeO-2PACz+TBA while maintaining ≈90% of its initial efficiency under continuous operation at 1-sun.

Interfacial Engineering with One-Dimensional Lepidocrocite TiO2-Based Nanofilaments for High-Performance Perovskite Solar Cells

The optimization of nonradiative recombination losses through interface engineering is key to the development of efficient, stable, and hysteresis-free perovskite solar cells (PSCs). In this study, for the first time in solar cell technology, we present a novel approach to interface modification by employing one-dimensional lepidocrocite (henceforth referred to as 1DL) TiO2-based nanofilaments, NFs, between the mesoporous TiO2 (mp TiO2) and halide perovskite film in PSCs to improve both the efficiency and stability of the devices. The 1DLs can be easily produced on the kilogram scale starting with cheap and earth-abundant precursor powders, such as TiC, TiN, TiB2, etc., and a common organic base like tetramethylammonium hydroxide. Notably, the 1DL deposition influenced perovskite grain development, resulting in a larger grain size and a more compact perovskite layer. Additionally, it minimized trap centers in the material and reduced charge recombination processes, as confirmed by the photoluminescence analysis. The overall promotion led to an improved power conversion efficiency (PCE) from 13 ± 3.2 to 16 ± 1.8% after interface modification. The champion PCE for the 1DL-containing devices is 17.82%, which is higher than that of 16.17% for the control devices. The passivation effect is further demonstrated by evaluating the stability of PSCs under ambient conditions, wherein the 1DL-containing PSCs maintain ∼87% of their initial efficiency after 120 days. This work provides not only cost-effective, novel, and promising materials for cathode interface engineering but also an effective approach to achieve high-efficiency PSCs with long-term stability devoid of encapsulation.

Tailored Polymer Hole-Transporting Materials with Multisite Passivation Functions for Effective Buried-Interface Engineering of Inverted Quasi-2D Perovskite Solar Cells

Although quasi-2D Ruddlesden‒Popper (RP) perovskite exhibits advantages in stability, their photovoltaic performance are still inferior to 3D counterparts. Optimizing the buried interface of RP perovskite and suppress energetic losses can be a promising approach for enhancing efficiency and stability of inverted quasi-2D RP perovskite solar cells (PSCs). Among which, constructing polymer hole-transporting materials (HTMs) with defect passivation functions is of great significance for buried-interface engineering of inverted quasi-2D RP PSCs. Herein, by employing side-chain tailoring strategy to extend the π-conjugation and regulate functionality of side-chain groups, target polymer HTMs (PVCz-ThSMeTPA and PVCz-ThOMeTPA) with high mobility and multisite passivation functions are achieved. The presence of more sulfur atom-containing groups in side-chain endows PVCz-ThSMeTPA with increased intra/intermolecular interaction, appropriate energy level, and enhanced buried interfacial interactions with quasi-2D RP perovskite. The hole mobility of PVCz-ThSMeTPA is up to 9.20 × 10-4 cm2 V-1 S-1. Furthermore, PVCz-ThSMeTPA as multifunctional polymer HTM with multiple chemical anchor sites for buried-interface engineering of quasi-2D PSCs can enable effective charge extraction, defects passivation, and perovskite crystallization modulation. Eventually, the PVCz-ThSMeTPA-based inverted quasi-2D PSC achieves a champion power conversion efficiency of 22.37%, which represents one of the highest power conversion efficiencies reported to date for quasi-2D RP PSCs.

Methylammonium-Free Ink for Blade-Coating of Pure-Phase α-FAPbI3 Perovskite Films in Air

The α-c (α-FAPbI3) has been extensively employed in the fabrication of high-efficiency perovskite solar cells, yet heavily relied on multiple additives in upscalable fabrication in air. In this work, a simple α-FAPbI3 ink is developed for the blade-coating fabrication of phase-pure α-FAPbI3 in ambient air free from any additives containing extrinsic ions. The introduction of 2-imidazolidinone (IMD) to the FAPbI3 precursor inks leads to the formation of intermediate phases that change the phase transition pathway from δ-FAPbI3 to α-FAPbI3 by tilting the PbI6 octahedrons with strong coordination to Pb2+. Furthermore, the IMD ligands in the intermediate phase gradually escape from the perovskite film during the annealing, leaving a phase-pure α-FAPbI3 film vertically grown with large grains. Consequently, the small-sized PSCs fabricated with blade-coated α-FAPbI3 film achieve an efficiency of up to 23.14%, and the corresponding mini-module yields an efficiency of 19.66%. The device performance is among the highest reported for phase-pure α-FAPbI3 PSCs fabricated in the air without non-native cations or chloride additives, offering a simple and robust fabrication approach of phase-pure α-FAPbI3 films for PV application.

All-In-One Additive Enabled Efficient and Stable Narrow-Bandgap Perovskites for Monolithic All-Perovskite Tandem Solar Cells

Hybrid tin-lead (Sn-Pb) perovskites have garnered increasing attention due to their crucial role in all-perovskite tandem cells for surpassing the efficiency limit of single-junction solar cells. However, the easy oxidation of Sn2+ and fast crystallization of Sn-based perovskite present significant challenges for achieving high-quality hybrid Sn-Pb perovskite films, thereby limiting the device's performance and stability. Herein, an all-in-one additive, 2-amino-3-mercaptopropanoic acid hydrochloride (AMPH) is proposed, which can function as a reducing agent to suppress the formation of Sn4+ throughout the film preparation. Furthermore, the strong binding between AMPH and Sn-based precursor significantly slows down the crystallization process, resulting in a high-quality film with enhanced crystallinity. The remaining AMPH and its oxidation products within the film contribute to improves oxidation resistance and a substantial reduction in defect density, specifically Sn vacancies. Benefiting from the multifunctionalities of AMPH, a power conversion efficiency (PCE) of 23.07% is achieved for single-junction narrow-bandgap perovskite solar cells. The best-performing monolithic all-perovskite tandem cell also exhibits a PCE of 28.73% (certified 27.83%), which is among the highest efficiency reported yet. The tandem devices can also retain over 85% of their initial efficiencies after 500 hours of continuous operation at the maximum power point under one-sun illumination.

Efficient and Stable Inverted Perovskite Solar Cells Enabled by Inhibiting Voids via a Green Additive

The buried interface in inverted perovskite solar cells (PSCs) is critical for determining device performance. However, during annealing, the perovskite crystallized downward from the film's top surfaces, and the use of dimethyl sulfoxide (DMSO) often resulted in voids at the perovskite bottom surface, which negatively impacted PSC performance. In this study, a green solid-state additive, piracetam (PA), was introduced into a perovskite precursor to reduce void formation. Due to the stronger interaction with perovskite components than DMSO, nonvolatile PA could remain within the perovskite films during thermal annealing to avoid volume collapse, thereby preventing the formation of voids at the buried interface as well as passivating the defects of undercoordinated Pb2+. Additionally, the introduction of PA could effectively enhance the crystallization of perovskite, leading to an improved quality of the perovskite films and depressed nonradiative recombination. As a result, the power conversion efficiency (PCE) of PSCs increased significantly from 20.95 to 23.42% with excellent operational and thermal stability.

Exploring the Potential and Hurdles of Perovskite Solar Cells with p-i-n Structure

The p-i-n architecture within perovskite solar cells (PSCs) is swiftly transitioning from an alternative concept to the forefront of perovskite photovoltaic technology, driven by significant advancements in performance and suitability for tandem solar cell integration. The relentless pursuit to increase efficiencies and understand the factors contributing to instability has yielded notable strategies for enhancing p-i-n PSC performance. Chief among these is the advancement in passivation techniques, including the application of self-assembled monolayers (SAMs), which have proven central to mitigating interface-related inefficiencies. This Perspective delves into a curated selection of recent impactful studies on p-i-n PSCs, focusing on the latest material developments, device architecture refinements, and performance optimization tactics. We particularly emphasize the strides made in passivation and interfacial engineering. Furthermore, we explore the strides and potential of p-i-n structured perovskite tandem solar cells. The Perspective culminates in a discussion of the persistent challenges facing p-i-n PSCs, such as long-term stability, scalability, and the pursuit of environmentally benign solutions, setting the stage for future research directives.

Surface n-Doped Metal Halide Perovskite for Efficient and Stable Solar Cells through Organic Chelation

Perovskite solar cells (PSCs) have emerged as a leading photovoltaic technology due to their high efficiency and low cost. Even though they have developed rapidly since their inception, with efficiencies of over 26%, inverted PSCs face challenges such as nonradiative recombination and ion migration. Surface treatment, especially the utilization of organic compounds, has improved efficiency and stability by optimizing the perovskite-charge transport layer interface. Herein, we report a facile and effective strategy by introducing 2,2'-bipyridyl to modify the surface of perovskite, achieving a power conversion efficiency of 24.43% with increasing open-circuit voltage and fill factor and good repeatability on multiple devices. We reveal that the 2,2'-bipyridyl molecule can chelate lead ions on the surface of perovskite, effectively suppressing nonradiative recombination. Furthermore, this modification can induce surficial n-doping to refine the energy level alignment, thereby minimizing charge transport losses. Additionally, the device maintained over 92% of the initial efficiency after 1000 h of operation at the maximum power point under continuous illumination. This surface chelation and defect passivation strategy employing 2,2'-bipyridyl offers a promising avenue for exploring the details of potential long-term degradation mechanisms and the development of commercially viable high-performance p-i-n PSCs.

Polymeric Charge-Transporting Materials for Inverted Perovskite Solar Cells

Inverted perovskite solar cells (PSCs) hold exceptional promise as next-generation photovoltaic technology, where both perovskite absorbers and charge-transporting materials (CTMs) play critical roles in cell performance. In recent years, polymeric CTMs have played an important role in developing efficient, stable, and large-area inverted PSCs due to their unique properties of high conductivity, tunable structures, and mechanical flexibility. This review provides a comprehensive overview of polymeric CTMs used in inverted PSCs, encompassing polymeric hole transport materials (HTMs) and electron transport materials (ETMs). the relationship between their molecular structures, modification strategies are systematically summarized and analyzed for adjusting energy levels, and improving charge extraction, enabling a deep understanding of these widely used materials. The review also explores effective strategies for designing even more efficient polymeric CTMs. Finally, an outlook is proposed on the exciting research of novel polymeric CTMs, paving the way for their commercialized applications in PSCs.

BCP Buffer Layer Enables Efficient and Stable Dopant-Free P3HT Perovskite Solar Cells

Poly(3-hexylthiophene) (P3HT) has garnered significant attention as a novel hole transport material (HTM). Principally, its cost-effective synthesis, excellent hole conductivity, and stable film morphology make it one of the most promising HTMs for perovskite solar cells (PSCs). However, the efficiency of PSCs employing P3HT remains less than ideal, primarily due to the mismatch of energy levels and insufficient interface contact between P3HT and the perovskite film. In this work, 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (BCP) was inserted into the P3HT/perovskite interface for effectively alleviating the recombination loss. BCP could effectively anchor uncoordinated Pb2+ and establish π-π stacking interactions with P3HT. These interactions not only neutralize flaws to reduce energy depletion but also enhance the configuration of P3HT, aiding in carrier transfer. Consequently, the BCP-modified device achieved an efficiency of 19.27%, which is significantly superior to the control device (12%).

Robust Imidazole-Linked Covalent Organic Framework Enabling Crystallization Regulation and Bulk Defect Passivation for Highly Efficient and Stable Perovskite Solar Cells

The low crystallinity of the perovskite layers and many defects at grain boundaries within the bulk phase and at interfaces are considered huge barriers to the attainment of high performance and stability in perovskite solar cells (PSCs). Herein, a robust photoelectric imidazole-linked porphyrin-based covalent organic framework (PyPor-COF) is introduced to precisely control the perovskite crystallization process and effectively passivate defects at grain boundaries through a sequential deposition method. The 1D porous channels, abundant active sites, and high crystallization orientation of PyPor-COF offer advantages for regulating the crystallization of PbI2 and eliminating defects. Moreover, the intrinsic electronic characteristics of PyPor-COF endow a more closely matched energy level arrangement within the perovskite layer, which promotes charge transport and thereby suppresses the recombination of photogenerated carriers. The champion PSCs containing PyPor-COF achieved power conversion efficiencies of 24.10% (0.09 cm2) and 20.81% (1.0 cm2), respectively. The unpackaged optimized device is able to maintain its initial efficiency of 80.39% even after being exposed to air for 2000 h. The device also exhibits excellent heating stability and light stability. This work gives a new impetus to the development of highly efficient and stable PSCs via employing COFs.

Cation reactivity inhibits perovskite degradation in efficient and stable solar modules

Perovskite solar modules (PSMs) show outstanding power conversion efficiencies (PCEs), but long-term operational stability remains problematic. We show that incorporating N,N-dimethylmethyleneiminium chloride into the perovskite precursor solution formed dimethylammonium cation and that previously unobserved methyl tetrahydrotriazinium ([MTTZ]+) cation effectively improved perovskite film. The in situ formation of [MTTZ]+ cation increased the formation energy of iodine vacancies and enhanced the migration energy barrier of iodide and cesium ions, which suppressed nonradiative recombination, thermal decomposition, and phase segregation processes. The optimized PSMs achieved a record (certified) PCE of 23.2% with an aperture area of 27.2 cm2, with a stabilized PCE of 23.0%. The encapsulated PSM retained 87.0% of its initial PCE after ~1900 hours of maximum power point tracking at 85°C and 85% relative humidity under 1.0-sun illumination.

Optical constants manipulation of formamidinium lead iodide perovskites: ellipsometric and spectroscopic twigging

Unraveling the knowledge of the complex refractive index and photophysical properties of the perovskite layer is paramount to uncovering the physical process that occurs in a perovskite solar cell under illumination. Herein, we probed the optical and photophysical properties of FAPbI3 (FAPI) and Cs0.1FA0.9PbI3 (CsFAPI) thin films deposited from pre-synthesized powder, by the spectroscopic ellipsometer and time-resolved fluorescence spectra. We determined the complex refractive index of perovskite films by fitting the measured spectroscopic ellipsometer data with the three-oscillator Tauc-Lorentz (T-L) model. We deduced that the CsFAPI thin film had a slightly lower absorption coefficient than the FAPI, but a higher refractive index and dielectric constant than the FAPI. The peak photoluminescence (PL) emission of FAPI and CsFAPI thin film on glass substrates was observed around 803 nm and 799 nm, respectively, while on ITO substrates, both FAPI and CsFAPI thin film was quenched and red-shifted to 816 nm. The methylammonium free pure CsFAPI-based perovskite solar cell fabricated in p-i-n configuration, measured a competitive efficiency of 16.14%, characterized by a J SC of 23.995 mA cm-2, V OC of 912 mV, and FF of 73.74%.

The Promise and Challenges of Inverted Perovskite Solar Cells

Recently, there has been an extensive focus on inverted perovskite solar cells (PSCs) with a p-i-n architecture due to their attractive advantages, such as exceptional stability, high efficiency, low cost, low-temperature processing, and compatibility with tandem architectures, leading to a surge in their development. Single-junction and perovskite-silicon tandem solar cells (TSCs) with an inverted architecture have achieved certified PCEs of 26.15% and 33.9% respectively, showing great promise for commercial applications. To expedite real-world applications, it is crucial to investigate the key challenges for further performance enhancement. We first introduce representative methods, such as composition engineering, additive engineering, solvent engineering, processing engineering, innovation of charge transporting layers, and interface engineering, for fabricating high-efficiency and stable inverted PSCs. We then delve into the reasons behind the excellent stability of inverted PSCs. Subsequently, we review recent advances in TSCs with inverted PSCs, including perovskite-Si TSCs, all-perovskite TSCs, and perovskite-organic TSCs. To achieve final commercial deployment, we present efforts related to scaling up, harvesting indoor light, economic assessment, and reducing environmental impacts. Lastly, we discuss the potential and challenges of inverted PSCs in the future.

Impurity-healing interface engineering for efficient perovskite submodules

An issue that affects the scaling-up development of perovskite photovoltaics is the marked efficiency drop when enlarging the device area, caused by the inhomogeneous distribution of defected sites1-3. In the narrow band gap formamidinium lead iodide (FAPbI3), the native impurities of PbI2 and δ-FAPbI3 non-perovskite could induce unfavoured non-radiative recombination, as well as inferior charge transport and extraction4,5. Here we develop an impurity-healing interface engineering strategy to address the issue in small-area solar cells and large-scale submodules. With the introduction of a functional cation, 2-(1-cyclohexenyl)ethyl ammonium, two-dimensional perovskite with high mobility is rationally constructed on FAPbI3 to horizontally cover the film surface and to vertically penetrate the grain boundaries of three-dimensional perovskites. This unique configuration not only comprehensively transforms the PbI2 and δ-FAPbI3 impurities into stable two-dimensional perovskite and realizes uniform defect passivation but also provides interconnecting channels for efficient carrier transport. As a result, the FAPbI3-based small-area (0.085 cm2) solar cells achieve a champion efficiency of more than 25.86% with a notably high fill factor of 86.16%. The fabricated submodules with an aperture area of 715.1 cm2 obtain a certified record efficiency of 22.46% with a good fill factor of 81.21%, showcasing the feasibility and effectualness of the impurity-healing interface engineering for scaling-up promotion with well-preserved photovoltaic performance.

Lead Iodide Redistribution Enables In Situ Passivation for Blading Inverted Perovskite Solar Cells with 24.5% Efficiency

Blade-coating stands out as an alternative for fabricating scalable perovskite solar cells. However, it demands special control of the precursor composition regarding nucleation and crystallization and currently exhibits lower performance than the spin-coating process. It is mainly the resulting film morphology and excess lead iodide (PbI2) distribution that influences the optoelectronic properties. Here, the effectiveness of introducing N-Methyl-2-pyrrolidone (NMP) to regulate the structure of the perovskite layer and the redistribution of PbI2 is found. The introduction of NMP leads to the accumulation of excess PbI2, mainly on the top surface, reducing residual PbI2 at the perovskite buried interface. This not only facilitates the passivation of perovskite grain boundaries but also eliminates the potential degradation of the PbI2 triggered by light illumination in the perovskite buried interface. The optimized NMP-modified inverted perovskite solar cell achieves a champion efficiency of 24.5%, among the highest reported blade-coated perovskite solar cells. Furthermore, 13.68 cm2 blading perovskite solar modules are fabricated and demonstrate an efficiency of up to 20.4%. These findings underscore that with proper modulation of precursor composition, blade-coating can be a feasible and superior alternative for manufacturing high-quality perovskite films, paving the way for their large-scale applications in photovoltaic technology.

High-Efficiency Inverted Perovskite Solar Cells via In Situ Passivation Directed Crystallization

Lead halide perovskite solar cells (PSCs) have emerged as one of the influential photovoltaic technologies with promising cost-effectiveness. Though with mild processabilities to massive production, inverted PSCs have long suffered from inferior photovoltaic performances due to intractable defective states at boundaries and interfaces. Herein, an in situ passivation (ISP) method is presented to effectively adjust crystal growth kinetics and obtain the well-orientated perovskite films with the passivated boundaries and interfaces, successfully enabled the new access of high-performance inverted PSCs. The study unravels that the strong yet anisotropic ISP additive adsorption between different facets and the accompanied additive engineering yield the high-quality (111)-orientated perovskite crystallites with superior photovoltaic properties. The ISP-derived inverted perovskite solar cells (PSCs) have achieved remarkable power conversion efficiencies (PCEs) of 26.7% (certified as 26.09% at a 5.97 mm2 active area) and 24.5% (certified as 23.53% at a 1.28 cm2 active area), along with decent operational stabilities.